The present invention concerns methods of determining impulse responses from a medium in relation to the transmission of waves between different points.
More particularly, the invention relates to a method of determining impulse responses of a medium in relation to the transmission of waves between different points, method comprising:
(a) at least one step of emission in the course of which waves are emitted into the medium by generating signals ei(t) on the basis of a number N of emission points belonging to the medium, where N is an integer at least equal to 2 and i is an index lying between 1 and N which designates one of said N emission points,
(b) at least one step of reception in the course of which signals rj(t) are picked up from said waves after transmission in said medium, at a number M of reception points belonging to the medium (these reception points may be coincident with the emission points), where M is a non-zero natural integer and j is an index lying between 1 and M which designates one of said M reception points,
(c) and at least one step of determination of said impulse responses hij (t) between each emission point i and each reception point j on the basis of the signals emitted ei(t) and picked up rj(t).
The impulse responses may be determined for the purposes of focusing waves in the medium, for example for the purposes of imaging the medium or of selective communication between various points of the medium, in particular within the framework of the implementation of the “D.O.R.T.” procedure (Décomposition de l'Opérateur Retournement Temporel [Decomposition of the Time Reversal Operator]) described in particular by Prada et al., (C. Prada and M. Fink, “Eigenmodes of the time reversal operator: a solution to selective focusing in multiple-target media.” Wave Motion, 20, pp 151-163 (1994)).
The process of acquisition of the impulse responses between the points in question of the medium is, however, relatively slow, insofar as it is performed sequentially, for the various emission points i one after the other, as described for example in the document WO-A-02/32 316 within the framework of a method of focusing of acoustic waves other than the abovementioned “D.O.R.T.” procedure.
This slowness lengthens the time of implementation of the method, and when the medium is changeable, it does not make it possible to obtain the impulse responses quickly enough to be able to be used validly thereafter in this medium.
The present invention is aimed in particular at alleviating these drawbacks.